Disk drives are well-known components of computer systems. Advances in disk drive technology have led to substantial increases in storage capacity and faster access times. Along with the increased capacity and speed, customers are also demanding consistency in drive-to-drive performance.
Original equipment manufacturers typically set specific performance requirements for drives supplied by various vendors in a given drive generation. These performance requirements generally involve a 4% to 40% generation-to-generation performance improvement for each of several specific tests. In addition to meeting these requirements, drive vendors must insure that drive-to-drive variation requirements are also met. Typically, all drives from a single HDD supplier should perform within 5% of the overall supplier's mean performance. As data densities have typically doubled each generation, the challenge of manufacturing drives that yield similar performance is receiving a great deal of attention.
In order to meet the 5% drive-to-drive performance variation requirement, vendors can either select very achievable (i.e., low performance threshold) targets and “slow down” drives that exceed these requirements, or implement performance testing and passing criteria for use in the manufacturing process. Typically, generation-to-generation improvement requirements and the goal of being the best-of-breed vendor force disk drive manufacturers to shoot for very challenging performance targets. Therefore, vendors typically do not have much extra performance margin relative to the targets and do not have the luxury of reducing performance of faster drives to lower the mean performance.
In recent hard disk drive generations, performance tests and corresponding passing criteria have been put in place for use during the manufacturing process. Drives that do not pass the criteria after manufacturing are considered manufacturing fails and count against the overall drive yields. Overall drive manufacturing yields typically range from 40% to 80% depending on the number of heads and disks contained in the disk enclosure. These performance tests insure that the drive variation requirements are met by the overall drive population. The impact of the performance tests on the overall yields vary, but a yield reduction of 5% is typical for a given drive generation.
One problem with testing performance during the manufacturing process involves the cost and time requirements. This testing procedure requires approximately ten minutes, but there are a limited number of testing slots available at a given time, so the time requirements are even more significant. In addition to the raw time requirements, the equipment required to test drives on a large scale is very costly. Performance requirements are usually set for a workload that is very susceptible to drive variations and involves a specific queue depth. In order to maintain a certain queue depth (usually 16), a relatively fast initiator system must be used. Although manufacturing testers supply one initiator system per drive, the testers and testing software typically are not optimized for performance. For example, the test suite is typically executed from a script that may not be precompiled. For this relatively slow initiator system, it is difficult to maintain the desired drive queue depth for many workloads. This makes testing some workloads very difficult. As drive performance continues to improve, this problem becomes more and more severe, thus stressing tester requirements.
Thus, there is a need for a method and apparatus for testing the performance of disk drives during manufacturing which reduces equipment and time requirements.